Method for distilling oils



Feb. 28 1939. w. w. KRAFT 2,149,058

METHOD FOR DISTILLING OILS Filed Nov. 15, 1935 Witness MEWWP Patented Feb. 28, 1939 UNITED STATES PATENT OFFICE METHOD FOR. DISTILLING OILS Wheaton W. Kraft, New York, N. Y., assignor to The Lummus Company, New York, N. Y., a corporation of Delaware Application November 15, 1935, Serial No. 49,933

2 Claims. (Cl. 196-73) The present invention relates to methods and turned to the column by a line 23, for reboiling apparatus for distilling oils. purposes, in place of or in conjunction with the It is well-known that the initial boiling point steam introduced at 8. Reboiling, instead of of any overhead distillate is not subject to consteam stripping, may be practised when the over- 5 trol, since it is determined by such light ends as head gasoline contains material which is not coni may be present in the charging stock. By ordidensable with the available cooling water. In nary methods, control of the initial boiling point such cases, the column is preferably operated can be effected only by making sure that the light under super-atmospheric pressure, and no steam ends are not present in the charging stock, but is used. Whether the distillation is carried out any such control is not commercially feasible, with steam, or by reboiling, or both, no attempt 10 since the preliminary removal of the light ends at complete separation in the primary column from a large body of charge material would reis made. quire an excessive quantity of heat and stripping The partially stripped or reboiled residue, steam. heated in the pipe still 22, is delivered to the The object of the present invention is to provaporizing zone of a second column 24, which 15 vide a method and apparatus whereby the initial has a bottom stripping zone 26 into which steam boiling point of any overhead distillate may be is introduced at 28. Above the point of introduceconomically controlled. With this object in tion of the heated oil, there are provided fracview, the present invention comprises the method tionating sections, indicated as three sections 30,

and apparatus hereinafter described and specifi- 32 and 34 and two side stripping sections 36 and 20 cally defined in the claims. 38. It will be understood that the number of The accompanying drawing is a diagram of the fractionating and side stripping sections may be preferred form of apparatus for practising the different from the number shown, depending on present invention. the number of side products to be removed.

The present invention is herein illustrated and Stripping steam is introduced into the sections 25 described as embodied in a system for obtaining 36 and 38 by pipes 40. naphtha of controlled initial boiling point, al- By fractionation, kerosene, accumulated in the though it may be applied to heavier fractions. section 32, passes through the side stripping sec- The crude oil is heated in a heat exchanger 2 tion 36 and is drawn off at 42 while naphtha or by other suitable means and passed to the accumulates in the section 34, passes through the 30 vaporizing zone of a column 4. The portion of side stripping section 38 and is drawn ofi at 44. the oil remaining unvaporized passes through a The initial boiling point of the naphtha at 44 is bottom stripping zone 6 into which steam is controlled by the stripping operation and the introduced at 8. Above the point of introduction end point by the fractionation provided in the of the crude, a series of fractionating decks l0 sections 32 and 30. 35 is provided, by which the end boiling point of the The vapo p in ou the p f the c lumn light gasoline product is controlled. The vapors are condensed in a condenser 46 and the conare condensed in a condenser l2 and the condendensate passed to a deca 48 m Which the sate is decanted at I4 to permit removal of water water is removed at 50. A part of the condenat l6, withdrawal of a light gasoline product at sate is returned by a pipe 52 as reflux to the 40 I8, and return of gasoline as reflux by the pipe 20. top of the fractionating section 34, whereby the The residue withdrawn from the bottom of control of the end boiling point of the naphtha the column 4 contains some of the components side product is effected. The remainder of the present in the light gasoline product withdrawn condensate is returned by a pipe 56 to the priat l8. If substantially complete removal of the mary column 4, preferably at a point at which 45 small quantity of light components from the the composition of the material in the column large body of residue were attempted, an uneapproximates that of the returned material. conomically large quantity of steam or a very Valved branch lines 58 permit introduction of considerable heating would be required. This the returned material to selected decks. The

would require increased refluxing in the fracmaterial returned by 56 includes components 50 tionating section of the column 4. According to within the boiling point range of the light gasothe present invention, no attempt is made to 'line product which is withdrawn at l8 and also effect complete separation in the column 4. components within the boiling point range of the The residue from the first column is heated in naphtha withdrawn at 44. When this material is a pipe still 22, from which a portion may be refractionated in the section II), it is so divided that 55 the components belonging in the light gasoline are vaporized and become part of the gasoline at [8, while the heavier components flow down the column into the residue which is withdrawn from the bottom of the column.

It will be seen that the control in the fractionating sections of both columns, namely, l0 and 34, is not critical, since components which are not initially allocated to their unique products find their way back to the first column for further separation.

The process offers the advantage of saving considerable steam and heat over any process in which substantially complete separation in the first column is attempted. Ordinarily, only a small quantity of material needs to be handled in the return pipe.

The present invention is particularly useful in the separation of light gasoline and naphtha where a low end point straight run gasoline has a high anti-knock value without additional processing but where the higher boiling components represented by a naphtha fraction must be cracked to obtain satisfactory anti-knock characteristios. For maximum efficiency, it is practically essential that the naphtha to be reformed have a controlled initial point, indicating the absence of components of low boiling point. Moreover, control of the end point of the light gasoline is necessary to make sure that this fraction does not contain material of lower antiknock value. The present invention accomplishes these results at little, if any, additional expense over the usual imperfectly controlled methods.

The present invention is not limited to gasoline but may be applied to any fractions, it being only necessary that the fraction which is to be controlled for initial point be withdrawn as a side product while the light ends are returned to a preceding step.

The invention having been thus described, what is claimed is:

1. The method of separating hydrocarbon mixtures by fractional distillation which consists in heating the mixture and feeding it to a primary fractionating column to obtain a low-boiling distillate as one fraction and a residue under conditions to incompletely remove from the residue materials within the boiling range of the low boiling distillate, heating the residue and passing it to a second column, condensing overhead material of the second column, refluxing in the second column with a part of said overhead condensate to condense a side stream, vaporizing from the side stream substantially all of the material within the boiling range of the low-boiling distillate, removing said side stream as another fraction of controlled initial boiling point, and conducting to the primary column above the point of feed of the original mixture the remainder of the second column overhead condensate which includes substantially all of the low boiling distillate components carried in the primary column residue and some of the components within the boiling range of said other fraction.

2. The method of separating hydrocarbon mixtures by fractional distillation which consists in heating the mixture and feeding it to a primary fractionating column to obtain a gasoline distillate and a residue under conditions to incompletely remove from the residue materials within the boiling range of the gasoline distillate, heating the residue and passing it to a second column, condensing overhead material of the second column, refluxing in the second column with a part of said overhead condensate to condense a naphtha side stream, vaporizing from the side stream substantially all of the material within the boiling range of the gasoline distillate, and conducting to the primary column above the point of feed of the original mixture the remainder of the second column overhead condensate which includes substantially all of the gasoline components carried in the primary column residue and some of the components within the boiling range of the naphtha side stream.

WHEATON W. KRAFT. 

